The present invention relates to a liquid ejection head and a method of manufacturing the same.
The liquid ejection head ejects pressurized liquid from a nozzle orifice as a liquid droplet, and the heads for various liquids have been known. An ink jet recording head is representative of the liquid ejection head. Here, the related art will be described with the ink jet recording head as an example.
An ink jet recording head (hereinafter, referred to as “recording head”) used as an example of a liquid ejection head is provided with a plurality of series of flow paths reaching nozzle orifices from a common ink reservoir via pressure generating chambers in correspondence with the orifices. Further, the respective pressure generating chambers need to form by a fine pitch in correspondence with a recording density to meet a request of downsizing. Therefore, a wall thickness of a partition wall for partitioning contiguous ones of the pressure generating chambers is extremely thinned. Further, an ink supply port for communicating the pressure generating chamber and the common ink reservoir is more narrowed than the pressure generating chamber in a flow path width thereof in order to use ink pressure at inside of the pressure generating chamber efficiently for ejection of ink drops.
To form the pressure generating chambers and the ink supply ports having such minute structures with high dimensional accuracy, very fine forging work is performed on a metal material plate (see Japanese Patent Publication No. 2000-263799A, for example).
As shown in FIG. 20, the pressure generating chambers are produced by forming a large number of elongated recess portions 71 in a metal material plate 70. The elongated recess portions 71 are formed by pressing the material plate 70 between dies, that is, a first die 72 and a second die 73. In the first die 72, a large number of projections 74 for formation of the elongated recess portions 71 are arrayed parallel with each other and gap portions 76 for formation of partition walls 75 of the pressure generating chambers are provided between the projections 74.
FIG. 20 shows a state that the material plate 70 is pressed by the first die 72 and the second die 73. When the projections 74 of the first die 72 are dug into the material plate 70, the material close to array-end projections 74 flows plastically in a direction indicated by arrows 77. As this plastic flow occurs, forces of pushing the tip ends of the array-end projections 74 in the arrayed direction thereof act on those projections 74 as indicated by arrows 78. When such forces are applied, stress is concentrated on the base portion of each projection 74 and cracks 79 may develop, possibly breaking a projection 74. Cracks 79 may develop in a relatively small number of projections 74 close to the end of the array of projections 74.
When cracks 79 develop or a projection 74 is broken, the elongated recess portions 71 are not formed in a prescribed shape. Since the life of the dies is shortened, the dies need to be replaced frequently, which is uneconomical in terms of the equipment costs. Another problem is that die replacement work lowers the productivity.